In fast neutron nuclear reactors, the liquid coolant of the primary circuit, which sends the calories provided by the fission reaction to the heat exchanger, is liquid sodium. So that such reactors may function properly, it is necessary to continuously monitor the quality of the sodium circulating in these circuits. In particular, it is essential to monitor any possible precipitation of sodium oxide and hydride crystals into the sodium itself. Having regard to the fact that the solubility of these impurities decreases when the temperature of the sodium drops, it is possible, by creating a cooling point around a calibrated hole of a sodium circuit, to provoke crystallization of any possible impurities. Such a crystallization causes the flow of sodium to reduce, which may be measured simultaneously with the temperature. Thus, a correlation has been established between the clogging temperatures of the sodium and the oxide and hydride percentages contained in the latter.
This principle is used by clogging indicators which determine the clogging temperature below which sodium oxide and hydrides start to precipitate.
Generally speaking, a clogging indicator is connected in parallel on a main pipe at the terminals of a diverter so that the flow of the branch circuit connection section is independent of any pressure fluctuations in the main pipe. The indicator itself mainly includes a contracted section where clogging is caused by cooling and where the evolution of the temperature and the flow of sodium in the branch circuit connection is simultaneously monitored. To this effect, a ventilation heat exchanger surrounds the clogging indicator which includes as a measuring member at least two thermoelements and two flowmeters. A filter may be placed at the inlet of the clogging indicator. At the outlet of the indicator, the sodium derived from the branch circuit connection or bypass pipe is remixed with the sodium of the main pipe.
In circuits carrying liquid sodium, the unclogging of the contracted measuring section is an extremely long operation and is often impossible when said section is completely clogged by impurities. In fact, in the event of a complete clogging, it is not possible to unclog the orifices without dismantling this contracted section, and even when clogging is only partial, after a normal functioning measurement, the time for dissolving the crystallized impurities is extremely long.
The object of the invention is to resolve these drawbacks by providing a clogging indicator, the unclogging of the orifices of the measuring section not requiring any dismantling or complete change of the device and making it possible to reduce the time for dissolving any impurities after each measurement.